GPT and obesity due to melanocortin 4 receptor deficiency: However, when exploring the relationship according to weight group, B12 was significantly associated with AST and ALT only in the extreme groups, i.e., in underweight (r = 0.22 and 0.24, p = 0.002 and <0.001, respectively) and severe obesity groups (r = 0.24 and 0.32, p = 0.002 and <0.001).